From European Patent No. 41 168, a temperature measuring sensor is known, having a quartz oscillator as its temperature-sensitive element, which is accommodated in a sealed metal housing, which has helium, for example, as a filling gas. The electrical line ducts leading through the housing wall are sealed off by the glass sleeves that surround them and are electrically insulated from the housing wall.
In practice, the dissimilar thermal expansion coefficients and heat-sensitive insulating materials make such seals problematic, especially at higher temperatures, so the line ducts limit the upper temperature measuring range of such temperature measuring sensors; also, such ducts are relatively expensive to produce.
One option for transmitting signals without a galvanic connection is known from German Patent Disclosure Document DE-OS No. 33 18 538, which describes a signal transmission by means of an inductive coupling of two coils, The differentiating effect of the coils is utilized for transmitting the edges of a digital signal. This patent disclosure document relates expressly to the weak coupling of a stray field, so that it is unsuitable for use in oscillators, which require the best possible coupling.